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Mk <br /> iHarding Lawson Associates <br /> r <br /> initial start-up period and by the' SJAPCD. Some provisions may <br /> be required to prevent, ground-water intrusion into the vapor <br /> firfims extraction system during operation. <br /> A drawback to a soil-venting system at this site is <br /> that the vadose zone is composed of moist, clayey, silty soils, <br /> Which tend to minimize the effectiveness of any vapor extraction <br /> process. If a soil .venting system were installed, it would be <br /> best to locate it in the area of highest hydrocarbon concen- <br /> tration to maximize the system's effectiveness. <br /> s <br /> By itself, soil-venting is not an attractive alterna- <br /> tive for this site; however, a horizontal extraction drain system <br /> tJ, is ,being considered for remediation of ground water, with <br /> L` r" trenches located in the area of highest hydrocarbon concentra- <br /> tion. A soil-venting system could easily be "piggy-backed" onto <br /> ij <br /> the ground-water remediation design, maximizing the efficiency of <br /> i <br /> both systems while minimizing the costs. In such circumstances, j <br /> soil-venting. becomes an attractive alternative for this site. <br /> The soil-venting system could be installed in the same trenches, <br /> r <br /> .. several feet above ground-water extraction drains. This configu- <br /> ration wou!i help alleviate potential ' <br /> I P ground-water interference <br /> with the soil-ventin _ F <br /> g-system - This alternative -will be given <br /> Ks further.r:,nsideration: <br /> r <br /> } Y No action The rio-action alternative involves leaving <br /> s k <br /> : ,a soils in place and instituting no remedial activities. Potential <br /> khw s movements of hydrocarbon constituents in soil would have to. be <br /> 3 <br /> i <br /> evaluated, along: with .resulting impacts on human, plan:, and <br /> to <br /> 19 <br /> Vf ? - <br /> XkEa _ <br /> r k7h� <br />